This invention relates to a control for actuating the spring brake of an electronically controlled braking system if there is an electrical failure.
Braking systems for heavy vehicles typically rely upon pneumatic air for actuation and control of actuation. Traditionally, when an operator steps on the vehicle pedal, a hydraulic or mechanical control supplies air to a service brake chamber of a two-chamber brake actuator. The air actuates a rod to set the brake.
Certain of the brake actuators are provided with a second spring brake chamber having a heavy spring which sets the brake under two conditions. This type of brake is known as an emergency brake, parking brake or simply a spring brake. In a non-actuated mode, air is supplied to a chamber beneath the spring to hold the spring at a non-actuated position. When an operator wishes to move the brake actuator to a parking brake position, the air is relieved and the spring sets the brake. Similarly, should there be a failure in the air system, the air will no longer hold the spring at its non-actuated position, and the spring sets the brake. This is the emergency brake function.
Recently, electronically controlled braking systems have been designed. In these braking systems, an operator's foot movement on the brake pedal creates an electrical signal that causes air flow to the service chamber which applies the brake. Typically, an electrical signal is sent to an air valve to allow air to pass into the service brake chamber.
Electronically controlled brakes are still provided with a spring brake chamber actuated upon parking or failure of air, to set the brake.
No acceptable solutions have been provided, however, for adapting to the problem of an electrical failure. That is, since the controls are electrical, if there is a failure in the power or control line or in the functioning of the associated electronic controls, then the brakes would no longer be functioning.
In the past, it has been proposed to supply redundant pneumatic controls to replace the electric controls in this event of system failure. This is complex and expensive.